The present invention provides blends of other thermoplastic resins that exhibit compatibility and have high heat distortion temperatures, which blends are formed from chlorinated polyvinyl chloride resins and styrene-maleic anhydride resins. Where the chlorinated polyvinyl chloride resin is present in the blend in an amount of forty percent or more, and the blend exhibits an oxygen index of at least 0.25, flame retardancy is also exhibited by the blends.
The formation of various blends of other thermoplastic compositions to produce a product which has beneficial properties for specific end uses has been effected. In such end uses, some properties of specific importance can be a high heat distortion temperature, as well as flame retardancy. Some such blends evidence compatibility over various ranges of respective resins, while some blends are not compatible with each other except under specific conditions. The present thermoplastic blend provides a product which is fully compatible and which is usable in applications where a high heat distortion temperature is required, and some of the products exhibit flame retardancy. In the formation of thermoplastic siding for use as a building covering, for example, such products may be used which have flame retardancy, as well as high heat distortion temperature, i.e., a heat distortion temperature in excess of about 200.degree. F.
The formation of blends of polyvinyl chloride resins has been previously taught, for example, in U.S. Pat. No. 3,626,033, which teaches the formation of ternary blends of a polyvinyl chloride resin, a polydiene rubber nitrile graft copolymer and an alkenyl aromatic/unsaturated anhydride copolymer. The formation, however, of blends of a chlorinated polyvinyl chloride resin and a styrene-maleic anhydride resin to form the present blends is not taught or suggested therein.